It is probable the calculi or stones found in other animals may have a similar origin, as they are formed on mucous membranes, as those of the kidney and bladder, chalk-stones in the gout, and gall-stones; and are probably owing to the inflammation of the membrane where they are produced, and vary according to the degree of inflammation of the membrane which forms them, and the kind of mucous which it naturally produces. Thus the shelly matter of different shell-fish differs, from the courser kinds which form the shells of crabs, to the finer kinds which produces the mother-pearl. The beautiful colours of some shells originate from the thinness of the laminae of which they consist, rather than to any colouring matter, as is seen in mother-pearl, which reflects different colours according to the obliquity of the light which falls on it. The beautiful prismatic colours seen on the Labrodore stone are owing to a similar cause, viz. the thinness of the laminae of which it consists, and has probably been formed from mother-pearl shells. It is curious that some of the most common fossil shells are not now known in their recent state, as the cornua ammonis; and on the contrary, many shells which are very plentiful in their recent state, as limpets, sea-ears, volutes, cowries, are very rarely found fossil. Da Costa's Conchology, p. 163. Were all the ammoniae destroyed when the continents were raised? Or do some genera of animals perish by the increasing power of their enemies? Or do they still reside at inaccessible depths in the sea? Or do some animals change their forms gradually and become new genera?] [_Echinus. Nautilus_. l. 67, 68. See additional notes, No. XXVII.] [_Pinna. Cancer_. l. 70. See additional notes, No. XXVII.] [_With worm-like beard_. l. 71. See additional notes, No. XXVIII.] [_Feed the live petals_. l. 82. There is a sea-insect described by Mr. Huges whose claws or tentacles being disposed in regular circles and tinged with variety of bright lively colours represent the petals of some most elegantly fringed and radiated flowers as the carnation, marigold, and anemone. Philos. Trans. Abridg. Vol. IX. p. 110. The Abbe Dicquemarre has further elucidated the history of the actinia; and observed their manner of taking their prey by inclosing it in these beautiful rays like a net. Phil. Trans. Vol. LXIII. and LXV. and LXVII.]